This is Hugelkultur, literally 'hill cultivation', and it's a central European practice, popular among permaculturalists, for creating a bed with lots of organic matter and microorganisms in it. The attraction for me was that it's a great way of making use of unwanted branches, of which I've generated quite a lot by cutting back overgrown shrubs recently. Basically, you build a heap with old wood at the base which breaks down gradually over a few years and turns into lovely crumbly, rich soil with a lot of the microlife that is so important for good cultivation. As it breaks down it ought to generate some heat to help boost whatever is growing on top.
The first problem was where to site it. My original idea was to put it up against the wall at the end of the vegetable garden, until I realised that next-door's cat would treat it as a convenient stepladder back to her own garden. Too close to the big ash tree at the side wouldn't be a good idea either; trees don't respond well to having soil piled up over their roots (although, because of the different levels between the neighbouring garden where the tree is growing and our plot, the tree must already be dealing with that problem). In the end I went for one of the square middle beds in the veg plot (ok, the only one of the middle beds that is actually completely usable, the rest still being at least partly overgrown), which is roughly the right size (1m square is the ideal). The actual construction has taken place gradually over the past few months, and is now in place and planted.
First, I dug out soil to a depth of 15-20cm. This generated quite a lot of bags of soil (which I still haven't dealt with!) but was easier than I expected. Then I put in the biggest branches. You're supposed to start with logs, but nearly all of what I had available was much smaller than that; the biggest piece was the big holly branch that came down in last year's gales. There were also a few other largish branches sitting in odd corners of the garden waiting to be dealt with; some of these were already rotting nicely, so I hope they will start the pile off on the right track. The rest came from cutting down an elder tree and the cutting back of a large viburnum. With hindsight, I probably ought to have backfilled this layer with some of the soil as there were quite a lot of gaps between the branches and I suspect the heap will fall in a bit as it breaks down.
Next came smaller branches, twigs, old buddleja canes, prunings, dead leaves, old cut-down stems from last year's perennials and general brushwood (photo shows this layer still in progress):
The next layer is supposed to be upturned turves, but my grass has far too many perennial weeds in for me to want to risk that. This doesn't sound like the sort of structure in which I will want to be digging out weeds. I think the idea is that this layer stops the soil from leaching through to the bottom layer, so I used last year's rotting grass clippings, which make a good dense cover.
Then some garden compost. The rotting wood will take nitrogen out of the heap, so there needs to be something to give sustenance to the plants growing on the top:
And finally a good layer of soil (from the stuff originally dug out of the bottom). I worried that this would just slide off, but it stayed put better than I expected.
Then: what to plant on it? The site isn't the sunniest spot, though it does get some sun. There's no point planting anything that requires rich soil, at least for a year or two, because of the nitrogen problem. Permaculturalists suggest potatoes, but I really can't imagine how you would dig into this heap without it falling apart! In the end I've put some courgette plants on there, and they're already starting to flower, which looks promising; and, whether because of the layer of Slug Gone round the plants or because the soil is too dry for molluscs, there's no slug or snail damage so far. Or maybe they don't like heights? A lettuce has now been added and I think I'll put some more saladings and maybe some annual flowers on there too.
Much of the wood at the bottom of the heap was generated by having to deal with the viburnums that were snow-damaged in the winter, and by cutting down the main stems of a big elder tree that had self-seeded in the shrubs at the side of the house. There is still work to be done here; once the choisya has finished flowering, it too is in line for the chop, and one of the osmanthuses needs the same treatment. These have all grown too big, with lots of evergreen foliage on the end of long woody branches, which should have been pruned back into shape long ago; in the event they were pulled down and broken by the snow before Christmas. The viburnum at the side of the house has been cut down to a much smaller, more manageable size (and will be pruned ruthlessly from now on!); I also found that one of the branches had layered itself and I've dug that up (rather roughly, but it seems to be surviving so far) and potted it on as I have plans for it. There is now a lot more light in that border and there's going to be much more planting space for ground-level plants, though just at the moment the area looks a bit like a lumber yard as there are still piles of smaller branches and twigs around (material for another Mountain in due course??!). There's also a big pile of soil and grit left over from some hard landscaping work here, and that needs weeding and spreading around to level things out. In due course there will be opportunities for more varied planting, with bulbs and perennials between the shrubs, and I'm working out what might work in there. Much of what is growing in this part of the garden is white- or light-flowered, so that it shows up in the dim light under the holly tree, and I think I'll keep that theme, but that still gives a lot of choice. Watch this space!
